Ever since re-watching ANH a couple weeks ago, I've been thinking a lot about everyone who could've known about Vader's past life as a Jedi by the time of Ep. IV.

First off, let's get the obvious ones out of the way:
-Palpatine
-Obi-Wan
-Yoda
There's no arguing with these characters, clearly.

Where it gets murky, however, is when you take these into consideration:
-R2-D2
-Owen & Beru
-Tarkin
-Yularen
-Bail Organa
With these characters, it's never explicitly stated they're completely in the know regarding Vader's alter-ego, so what do you think? Also, is there anyone I missed that I should add to the list?

R2 is probably the only character in the entire saga that knows, more or less, the whole story.

Owen & Beru knew. Look at their faces when Luke mentions Obi-Wan. Owen makes it very clear that he is to stay away from "old Ben" because of what happened to Luke's father. "He has too much of his father in him." "That's what I'm afraid of." Oh yeah, Owen knew and it scared the hell out of him. That's why he keeps Luke on the farm. He doesn't really need Luke for "one more season". He's being protective.

R2 is probably the only character in the entire saga that knows, more or less, the whole story.

Owen & Beru knew. Look at their faces when Luke mentions Obi-Wan. Owen makes it very clear that he is to stay away from "old Ben" because of what happened to Luke's father. "He has too much of his father in him." "That's what I'm afraid of." Oh yeah, Owen knew and it scared the hell out of him. That's why he keeps Luke on the farm. He doesn't really need Luke for "one more season". He's being protective.

I agree. But still, Lucas had no idea about that when he wrote and shot that scene. It plays out quite well in the end, and as much as I dislike Episode 2, I thought it was a good decision to insert the Lars in that way.

R2 is probably the only character in the entire saga that knows, more or less, the whole story.

Owen & Beru knew. Look at their faces when Luke mentions Obi-Wan. Owen makes it very clear that he is to stay away from "old Ben" because of what happened to Luke's father. "He has too much of his father in him." "That's what I'm afraid of." Oh yeah, Owen knew and it scared the hell out of him. That's why he keeps Luke on the farm. He doesn't really need Luke for "one more season". He's being protective.

I agree. But still, Lucas had no idea about that when he wrote and shot that scene. It plays out quite well in the end, and as much as I dislike Episode 2, I thought it was a good decision to insert the Lars in that way.

Oh yeah. Even more than that too. The novelization (I can't remember if it was for ANH or ROTJ) had Owen being Anakin's brother! There was definitely some backstory tension that GL wanted to reference in that scene, but I don't think even he knew what it would be in the end. He wasn't even committed to Anakin being Vader at that point. GL could have stayed true to old Ben's story about Vader killing Luke's father and the table scene with Owen still would have worked. It was deliberately ambiguous.

Oh yeah. Even more than that too. The novelization (I can't remember if it was for ANH or ROTJ) had Owen being Anakin's brother! There was definitely some backstory tension that GL wanted to reference in that scene, but I don't think even he knew what it would be in the end. He wasn't even committed to Anakin being Vader at that point. GL could have stayed true to old Ben's story about Vader killing Luke's father and the table scene with Owen still would have worked. It was deliberately ambiguous.

I think the ROTJ novel said Owen was actually Obi-Wan's brother. Not Anakin's

Oh yeah. Even more than that too. The novelization (I can't remember if it was for ANH or ROTJ) had Owen being Anakin's brother! There was definitely some backstory tension that GL wanted to reference in that scene, but I don't think even he knew what it would be in the end. He wasn't even committed to Anakin being Vader at that point. GL could have stayed true to old Ben's story about Vader killing Luke's father and the table scene with Owen still would have worked. It was deliberately ambiguous.

I think the ROTJ novel said Owen was actually Obi-Wan's brother. Not Anakin's

THAT'S RIGHT! Yes, thank you. I knew there was a weird connection to Owen in the novel that didn't materialize in the movie. A shame too. I always figured Owen had a lot more to do with the backstory than he eventually did in the prequels. Clearly there is a rift between him and Obi-Wan. I had hoped the prequels would have explored that. Oh well...

I don't think Owen and Beru knew that Anakin became Darth Vader. I don't think Obi-Wan told them, maybe because he figured if he did Owen and Beru wouldn't want to keep Luke. They defiantly didn't know to begin with, because Obi-Wan thought Anakin died on Mustafar. In Dark Lord: Rise of Darth Vader Obi-Wan considered warning them Vader was still alive them but Qui-Gon said there wasn't any need as Vader wouldn't ever return to Tatooine. I think that Owen and Beru considered the Jedi very dangerous and foolhardy and figured Anakin died with the rest of the Jedi.

R2D2 obviously knew the whole story, and Bail Organa defiantly knew as well. After that it's murky. Tarkin pieced it together but was never certain. The attitude he displayed towards Vader in ANH certainly suggested he knew Vader was once a Jedi.

The Clone Wars suggests it. Tarkin seems like the type that would thoroughly investigate his command team. Especially Vader, whom the Emperor expects Tarkin to yield substantial power and authority. Most assume Vader is subservient to Tarkin, but I don't think it was that kind of arrangement at all. Tarkin was in command of the Death Star whereas Vader was not part of the military command structure- he was representative of the Emperor. This gave Vader a lot of freedom that most Death Star senior officers resented, but Tarkin understood Vader's worth. Vader also respected Tarkin, incredible given his usual temperament to most Imperial Officers.

I don't think Tarkin knew Anakin was Vader but I think he knew that he was once a Jedi. Tarkin doesn't really like Vader, IMO, and I think it shows how he dismisses the 'old religion'.

Bail Organa certainly knew. I think he made sure that Leia would be ready to face the Empire as best she could. Out of the whole galaxy, I think only 4 living people knew the absolute truth.

The Lars... they may have been told at some point, but I don't think they did. They certainly knew about the rise of the Empire and the fall of the Jedi and because Obi-Wan was one of the survivors they probably blamed him for Anakin's 'death' for not being able to save him when he should have lived.

I'd say Tarkin knows. When Tarkin asks Vader what makes him think Kenobi is on the Death Star, Vader says "a Tremor in the Force. The last time I felt it was in the presence of my old master".

I gotta agree here too as Tarkin as we know, and this is not counting the The Clone Wars cartoon were Anakin and Tarkin are shown on a mission, Tarkin is Shown at the end of ROTS so here therefore was serving In the Republic navy during the clone wars. We know Anakin was known as Obi-wans former Padawan so even if Tarkin did not know before that scene in A New Hope he would obviously put 2 and 2 together and knew after that scene.

Tarkin knew, certainly. Even if not from the very beginning (ie end of ROTS) then he found out soon afterwards.
He's certainly not the type to go "Oh, a random huge evil cyborg. *shrug* Eh, who cares."

Did Bail even know? If Obi-Wan didn't tell Owen and Beru, it's doubtful he told Bail (and we can't be sure he would). I'm still unsure whether Obi-Wan knew Anakin/Vader had survived at the end of ROTS, and, if he doesn't, it's not unfeasible to think he only realised when he got to the Death Star in ANH.

Bail figured it out, in that Darth Vader book.
Even if Obi-Wan didn't know Vader was alive by the end of ROTS I'm pretty sure he figured it out when he caught the first news holofeed with this guy named Vader standing around beside Palpatine

Which was in the "Darth Vader book" you mentioned- Dark Lord: The Rise of Darth Vader.

Though I suspect that Bail knew in RoTS. In the aftermath of the fight on Mustafar, Yoda and Ben may have filled him in on the details- so when he sees a suited "Darth Vader" not long afterward, he knows exactly who it is.

But is Vader even in an official role? He's basically a henchman... he has no official role as far as I can see with regards to The Empire. Those directly involved in command would be aware of him, yes, but I always thought of Vader as being more like a secret agent - an enforcer. Whether he'd feature in any News Holofeed is debatable, and even then, Obi-Wan (living as a hermit in relative quiet and seclusion) needs to be made aware of it. Then again, Leia knows who he is ANH, but that's perfectly conceivable without the general public being aware.

The EU went out of its way to paint him as a very high profile figure- the Emperor's iron fist, in short. With him being Supreme Commander of Imperial Forces at one point- which is one of the reasons he can Force-choke admirals with impunity in ESB.

I think the ROTJ novel said Owen was actually Obi-Wan's brother. Not Anakin's

Can't remember that. He said that he's going to send Luke at Tatooine and look after him but as an egocentric uncle, not a father. Don't have any idea if Owen and Beiru knew it.

Ben, Yoda and Palps certainly knew. Bail Organa very likely knew it too, in fact I think that it's almost certain that he knew. Tarkin could have known too but probably later, I think that in The Force Unleashed II novel he doesn't knew about Anakin being Vader but I could be wrong. Doubt that anyone else knew about it.

But is Vader even in an official role? He's basically a henchman... he has no official role as far as I can see with regards to The Empire. Those directly involved in command would be aware of him, yes, but I always thought of Vader as being more like a secret agent - an enforcer. Whether he'd feature in any News Holofeed is debatable, and even then, Obi-Wan (living as a hermit in relative quiet and seclusion) needs to be made aware of it. Then again, Leia knows who he is ANH, but that's perfectly conceivable without the general public being aware.

An enforcer, yes. Not exactly a secret one.
From what I gather, his "official role" is whatever the hell the Emperor tells him to do. That can vary from hunting a lone fugitive on foot to commanding his own fleet as in ESB.
As
@Iron_lord mentioned, he was also the Supreme Commander at one point, making him second in command officially as well as in practice. But, no matter the title, he pretty much is second in command, unless Emperor tells him he's not.

EDIT - As far as general public goes, I honestly have no idea. To me, it makes sense to have Vader be a visible figure of power and authority and on the other hand I'm sure it would raise a few eyebrows. On the third hand, the Emperor might not bloody well care how much eyebrows it rasies haha.
I'm pretty much sure that the public was aware of Vader's existance and that he was high up in the chain of command.